Andrea Arcangeli 11feeb4980 kvm: optimize away THP checks in kvm_is_mmio_pfn() ... The checks on PG_reserved in the page structure on head and tail pages aren't necessary because split_huge_page wouldn't transfer the PG_reserved bit from head to tail anyway. This was a forward-thinking check done in the case PageReserved was set by a driver-owned page mapped in userland with something like remap_pfn_range in a VM_PFNMAP region, but using hugepmds (not possible right now). It was meant to be very safe, but it's overkill as it's unlikely split_huge_page could ever run without the driver noticing and tearing down the hugepage itself. And if a driver in the future will really want to map a reserved hugepage in userland using an huge pmd it should simply take care of marking all subpages reserved too to keep KVM safe. This of course would require such a hypothetical driver to tear down the huge pmd itself and splitting the hugepage itself, instead of relaying on split_huge_page, but that sounds very reasonable, especially considering split_huge_page wouldn't currently transfer the reserved bit anyway. Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Gleb Natapov <gleb@redhat.com>		2013-08-27 11:01:10 +03:00
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kvm	kvm: optimize away THP checks in kvm_is_mmio_pfn()	2013-08-27 11:01:10 +03:00